Most concrete mixer units are adapted for handling either very low orders of slump in which the aggregate tends to be very stiff and has a low water content (such slumps being adapted for paving and for formless type pouring), or the transit mixer is adapted for relatively high slumps in which there is a more liquid type aggregate characterized by a high water content and in which the pour is generally made into a form. The difficulty lies in providing a single concrete mixer unit which can handle both orders of slumps. Heretofore the mixer has been particularly adapted for one or the other, but not for both. The obstacle to an all-purpose mixer lies in the inability of the bowl to effect a discharging action on stiff, low slump aggregates when the bowl is counterrotated to lift the aggregate from the interior of the bowl, from the base or lowermost bowl section and cause it to be lifted along the length of the bowl to the raised discharge end of the bowl. What happens is that if the bowl and unit are constructed to handle very stiff, low order magnitude slumps of aggregates, then when there is substituted a high slump, or fluid, mixture, the bowl, upon counterrotation, tends to effect too rapid discharge of such aggregate. Conversely, for drums which are adapted for very high slumps, the same drum, if loaded with a very low, stiff slump, is unable to discharge because the aggregate moves up the drum, then falls back, rather than emerging at the discharge end of the drum. Therefore, it is typical of the art that a transit concrete mixer unit, whether of the front discharge or rear discharge variety, is adapted for low or high slumps, but not for both.